An example of such a latching mechanism used in a convetional push switch shown in FIGS. 1-5. A casing 5 for the push switch receives a slider 1 received partially within the casing 1. The upper portion of the slider has a heart-shaped cam groove 1a and the lower portion forms a receiving portion 1f adapted to receive and retain movable contacts 4. The casing 5 of the switch has an opening 5a at its one end, and the receiving portion 1f is mounted in the casing 5 so as to be slidable. The movable contacts 4 received in the receiving portion 1f can be brought into sliding contact with fixed contacts 7, three on each side, extending vertically from an insulating plate 6 which is mounted to the bottom of the casing 5. The switch is so designed that as the slider moves, the manner of connection of the movable contacts with the three pairs of fixed contacts changes. The slider 1 is always biased in the direction indicated by the arrow B in FIG. 4 by a spring 8 whose outer end is held to the outer end of the slider. The inner end of the spring 8 is held to a retaining portion 5b formed on the front wall of the casing 5.
A driving pin 2 in the shape of a crank is disposed in the direction of movement of the slider 1. A hole 5c is formed in the top portion of the casing 5. A base plate 9 which is mounted to the underside of the top portion of the casing 5 is provided with a hole 9a extending through the plate. One end 2a of the pin 2 extends through the hole 9a, and is pivotally held in the hole 5c. The pin 2 further includes an intermediate portion 2b, and another end 2c is received in the cam groove 1a in the slider 1. The end 2c is biased into the cam groove by the leaf spring 3 formed by part of the base plate 9. The spring 3 is centrally provided with an elongated rib 3a which is disposed substantially perpendicularly to the longitudinal direction of the pin 2 when the base plate 9 is installed in the casing 5, in order to bias the pin 2 toward the slider.
In the single-acting mechanism used in the push switch constructed as described above, when the slider 1 is pushed inwardly in the direction indicated by the arrow A against the resilience of the spring 8 when the end 2c of the driving pin 2 lies at a position f of the cam groove, as shown in FIG. 3, the end 2c moves up along an inclined surface of the cam groove and reaches the position a. Further inward movement of the slider results in the end 2c of the pin falling downwardly at a step 1b to arrive at a position b. Since the pin 2 is biased in a direction indicated by the arrow D by the leaf spring 3, the end 2c moves from the position a to the position b without moving from the position a directly to the position d. Thereafter, the inward pressure on the slider is released and the slider 1 is latched in position as the end 2c reaches the position c. Upon the next inward movement of the slider, the end 2c of the pin falls at steps 1c, 1d, and 1e and passes across positions d and e. Finally, the pin returns to the original position f. As the slider 1 moves in this way, the movable contact 4 slides across the fixed contacts 7. Thus, the contact positions of the movable contact 4 with the three pairs of the fixed contacts 7 changes, thereby performing a switching action.
In the latching mechanism in the conventional switch constructed as thus far described, one end 2a of the driving pin 2 extends through the hole 9a in the base plate 9 and is pivoted in the hole 5c formed in the top portion of the casing 5, whereas the other end 2c is received in the heart-shaped cam groove 1a in the slider 1 and biased by the leaf spring 3 fabricated from the base plate 9. Therefore, the pin 2 is required to have a cranklike form. Further, since the pin 2 is shaped like a crank and has an end disposed upright from the direction of movement of the slider, it is necessary to make the height of the casing 5 equal to the height of the pin 2. These limitations have made it considerably difficult to fabricate the push switch employing such a locking mechanism into a small-sized or thin structure.
In addition, when the driving pin 2 is inserted into the hole 9a in the base plate 9 and mounted into the hole 5c formed in the top portion of the casing 5, one end 2a of the pin 2 must be inserted into the hole 5c in accordance with the procedures illustrated in FIG. 5 before it is mounted in the top portion. Thus, the assembly operation involves many steps. Accordingly, the mechanism is fabricated in an inefficient way, increasing costs.